It is well-known that washing machines must be equipped with devices which can lock the door closing mechanism when the machine is started up and then unlock them with a certain delay after the current has switched off, in order to ensure that the door cannot be opened while some of the components are still rotating inertially (in particular the drum of the spin-dryer).
Some types of these devices exist in which the closing and delayed opening is obtained by means of the use of a bi-metal and the time this takes to cool. There are other types of devices, some of them of the same inventor, which carry out the aforesaid functions by other means: magnetic, wax actuated thermostats etc.
It is also known from French Pat. No. FR-A-2 477 620 to actuate a locking pin that with its movement locks the door closure latch, by using the motion of the mobile contact of a microswitch, wherein the support of the mobile contact is made of two half pieces joined by a spring and is actuated by two opposite and curved bi-metallic elements.
With such a system because of the instrinsic characteristics of the springs, said spring does not maintain its initial calibration so that connection and delay times vary with time and use. Furthermore, the calibration system of said patent, obtained by acting on the first half part of the support of the mobile contact, does not allow a sufficient calibration precision.
Finally, the presence in said patent of two opposite bi-metallic elements, in addition to doubling possibilities of errors, in particular conditions after a number of consecutive actuations, causes a kind of balance of the opposite forces, with the consequence of an insufficient thrust on the support of the mobile contact during actuation, so as to cause false contacts or lack of contact, and consequently said contacts stick together or burn out.
Furthermore a device is shown in EP-A-0 092 162 constituted by a sliding bar, working together with the hook of the door latch associated with a pin suitable for locking the aforesaid sliding bar under certain pre-set conditions, wherein the locking pin is actuated by the mobile contact plate of a microswitch, having also the funciton of a series switch, wherein the mobile contact of the microswitch is actuated by a single bi-metallic strip suitably heated and electrically connected to the controls of the machine, and wherein the heating means of the bi-metallic strip is constituted by a P.T.C.-resistance.
With this system the bi-metallic strip is fixed at one end to the mobile contact plate of the microswitch and acts on the mobile contact through a spring. Thus while it works well it does not maintain a sufficient calibration precision through time and there is also a certain difficulty involved in mounting the spring which connects the bi-metallic strip to the mobile contact plate.
The object of the present invention is to provide a door-locking device which gives ample guarantees of safety, locking the door before the washing machine is in motion, maintaining this lock during the time the machine is operating up to the time the current is interrupted and beyond this until every rotating part has stopped.
A further characteristic of the invention is that the door-locking device is equipped with an extremely simple and effective device which regulates the opening time.
Another characteristic of the invention is the arrangement of its components which makes it possible to construct and mount the body of the device and subsequently add to it the eyelet sliding bar into which the hook of the door-latch and the coupling flange of the washing machine fit. These details vary from manufacturer to manufacturer, therefore the same basic standard device can be used for the most varied types of machines simply by changing these two specific details (sliding bar and coupling flange).
Finally, it has been designed in such a way that the basic body of the door-locking device can, when requested, be connected up to a device which contains the controls of the moving parts of the machine during the washing stage, or to the drying controls if the machine also functions as a dryer, so that the door is not locked during these sequences of the cycle.
The apparatus according to this invention is basically constituted by a sliding bar, working together with the hook of the door closing mechanism, said sliding bar being combined with a pin which locks the aforesaid sliding bar under certain specific conditions, wherein the locking pin is actuated by the mobile contact plate of a microswitch, having the function of a series switch, and the mobile contact means of the microswitch is actuated by a single bi-metallic strip, suitably heated by a P.T.L. resistance electrically connected to the starting controls of the machine, characterized in that the mobile contact of the microswitch is actuated by means of a rocker arm interposed between the bimetallic strip and the mobile contact of the microswitch; and the appropriate part of the contact plate of the microswitch is, in its turn, subjected to the load of an eccentric ratchet; said load having the function, by increasing or decreasing, of altering the insertion time and the delayed opening of the door-lock as a function of the possible variations of the time of bending and straightening of the bi-metallic strip during the heating and cooling of the bimetal and the related heating equipment, variations which can occur even between materials of the same lot, and the bimetallic strip simply rests on supports located at each end and the P.T.C. resistance rests on it, just the rocker arm 6 rests on the P.T.C. resistance thus ensuring that the curvature and straightening times remain certain through time. The invention will become clearer if reference is made to the example of an embodiment, an example which is indicative and non-limiting, in the three drawings attached.